Although a variety of safety control systems have been known, they have no function to automatically check the entire user's gas conduit including the gas meter. They can check only a particular gas conduit portion. In accordance with conventional gas leakage checking methods, the gas leakage can be checked only when the internal pressure of the gas conduit is decreased to a certain pressure. For this reason, where gas is leaked in a low rate, one hour or more is taken to sense this gas leakage.
Taking into consideration the fact that the gas supplied to the home has a pressure ranging from 100 to 250 mmH.sub.2 O, the reference pressure for checking the gas leakage is typically determined to range from 50 to 80 mmH.sub.2 O. Since the actual average gas supply pressure is about 200 mmH.sub.2 O, a lot of time is taken for the pressure of the entire gas conduit to decrease from 200 mmH.sub.2 O to 50 mmH.sub.2 O.
In accordance with the conventional methods, gas leakage can be checked only after the user closes the gas valve because this checking is based on the internal pressure of the gas conduit. As a result, there is a problem that the user cannot use the gas while checking for leakage. This makes it impossible to check the gas leakage for a long period of time.
For systems having a function to check the hose connected between the gas conduit and the gas range, it is possible to achieve the checking in a short period of time. However, these systems cannot achieve the gas leakage checking for the entire gas conduit because the checking is limited to a particular gas conduit portion such as the hose or the gas range. For this reason, these systems are insufficiently safe.